Volodymyr Zelenskyy
Volodymyr ZelenskyyUkrainian Presidential Press Service/via Reuters TV/Handout via REUTERS

Ukrainian President Volodymyr Zelenskyy said on Monday night that Russian forces had begun a new offensive in eastern Ukraine, Reuters reported.

“We can now say that Russian forces have started the battle of the Donbas, for which they have long prepared,” he said in a video address.

His comments came after senior officials said Moscow had begun a new offensive push along most of Ukraine’s eastern flank.

Zelenskyy said that Russia had concentrated a significant part of its forces for the offensive.

“No matter how many soldiers are drawn there, we will defend ourselves. We will fight. We will not give up anything Ukrainian,” he stated.

On Sunday, a Russian ultimatum expired for remaining forces to surrender in the port city of Mariupol, but Ukraine vowed to fight to the end.

"The city still has not fallen," Prime Minister Denys Shmyhal said hours after Moscow's deadline had passed for fighters holed up and surrounded in a sprawling fortress-like steelworks to surrender.

"There's still our military forces, our soldiers. So they will fight to the end," he stated in an interview with ABC's "This Week".

Zelenskyy, meanwhile, warned on Sunday that Russia might use chemical or even nuclear weapons and urged world leaders to prepare for such contingencies.

Speaking with CNN in an interview, Zelenskyy said the potential use of chemical or nuclear weapons posed a threat to the entire planet, and urged foreign powers to prepare anti-radiation medicine and air raid shelters.

“Not only me – all of the world, all of the countries have to be worried because it can be not real information, but it can be truth,” he stated.